The present invention relates generally to blood filter and associated devices for temporary placement in a blood vessel to capture embolic material, and more particularly to a hollow vessel insertion device with an adjustable filter apparatus for placement in a blood vessel to carry blood to the vessel and to entrap embolic material in the vessel, for example when delivering blood to the aorta from a bypass-oxygenator system during cardiac surgery. The present invention also relates to methods for protecting a patient from embolization that may be caused by procedures, such as incising, clamping and unclamping, which may dislodge atheromatous material from an artery.
During cardiac surgery, it is often necessary to introduce a cannula into an artery or other blood vessel. For example, an arterial cannula is typically introduced into the aorta to deliver blood from a bypass-oxygenator system. Such a cannula generally includes a proximal end for receiving blood from a bypass-oxygenator machine, a distal end for entry into an artery and a lumen extending between the proximal and distal ends.
One concern with such procedures is that calcified plaque or other embolic material may be dislodged, particularly when clamping or unclamping arteries such as the aorta. See Barbut et al., xe2x80x9cCerebral Emboli Detected During Bypass Surgery Are Associated With Clamp Removal,xe2x80x9d Stroke, 25(12):2398-2402 (1994), which is incorporated herein by reference in its entirety. Such embolic material may travel downstream, possibly becoming lodged in another portion of the blood vessel or possibly reaching a vital organ, such as the brain, where the material can cause substantial injury to the patient.
For this reason, some arterial cannulas may include a blood filter device attached directly to them. For example, an expandable filter device may be mounted on the distal end of a cannula, allowing the filter to capture any loose embolic material once the cannula is introduced into the vessel. Generally, such devices include an expandable frame, such as an inflation seal or an umbrella frame, and a filter mesh attached to the frame, the mesh being adapted to capture embolic material of a predetermined minimum size. The frame may be attached externally to the distal end, or alternatively, it may be retractably deployed from a lumen within the cannula.
The use of a cannula with such a filter device, however, may not be as effective as desired. For example, because the filter is generally attached to the distal end of the cannula, the filter may be exposed within the vessel for the entire duration of the procedure, sometimes several hours. Because of the length of time of most cardiac procedures, the filter mesh may eventually become clogged due to thrombus formation or buildup of embolic material, preventing the device from effectively capturing additional material and/or possibly impairing blood flow through the filter. If the filter is retractable, it may be closed within the vessel when it becomes clogged, but this prevents capture of embolic material throughout the remainder of the procedure.
Accordingly, there is a need for a filter device for use with an arterial cannula or other hollow vessel insertion device, such as an introducer, that minimizes the exposure of the filter within a blood vessel, thereby reducing the risk of clogging the filter mesh. Certain types of self-expanding modular filter devices have been described in U.S. Pat. No. 5,846,260, which is incorporated herein by reference in its entirety. However, there is a need for a modular filter apparatus with a filter that can be adjusted to fit various sizes of vessels. The exterior of such a device should optimally conform to the size and shape of the inner lumen of the vessel through which the emboli may pass to reduce the possibility of emboli escape around the exterior of the filter. The size of such a filter should be either self-adjusting or adapted to external operation to adjust the size to fit the vessel in which the filter resides. Further, there is a need for associated devices such as vessel sizing tools, expandable obturators, cannula liners and blood filtering system indexing/locking devices to assist in the use of the blood filtering system.
The present invention is directed to a modular adjustable blood filter device and a delivery system for intermittently introducing the filter device into a blood vessel during an extended surgical procedure and to methods for using such a device. The present invention is also directed to a hollow vessel insertion device, such as an introducer or an arterial cannula, with modular filter device for temporary placement in a blood vessel to carry blood to the vessel and to entrap embolic material in the vessel, for example when delivering blood to the aorta from a bypass-oxygenator system during cardiac surgery.
Generally, an embodiment of a blood filtering system includes a modular filter apparatus and a hollow vessel insertion device, such as an arterial cannula or an introducer, capable of receiving the filter for capturing embolic material in a blood vessel. The insertion device may be a stand-alone device, or may be part of a blood filtering system with the modular filtering apparatus. When the insertion device and the filter are used together, certain embodiments include indexing and locking mechanisms to assure proper alignment of the filter in the device. These indexing/locking mechanisms may also be included when the insertion device is used with other apparatuses, for example obturators.
When a cannula is used, it has a distal end adapted to enter an artery, a proximal end adapted to receive blood from a bypass oxygenator machine, and a lumen that extends from the proximal end to the distal end. The cannula can be a hybrid of extruded, drawn or welded metal tubing and molded or machined plastics, or could be made entirely of metal or of plastic. The cannula also includes a port for receiving the modular filter apparatus. The port may be attached to or integrally formed on the outer surface of the cannula, the inner surface of the cannula, such as a lumen parallel with the main cannula lumen, possibly on the front (downstream area), back (upstream area) or side of the cannula. Preferably, a side port is located adjacent the distal end of the cannula, for example above a suture flange thereon. More preferably, the side port extends diagonally from the outer surface to facilitate directing the filter device towards the distal end of the cannula. A passage extends from the side port to the lumen in the cannula, or alternatively, may extend distally from the side port along a wall of the cannula to an outlet on or adjacent the distal end of the cannula. The side port may include a hemostatic valve across the passage to provide a fluid-tight seal, yet allow a modular filter cartridge to be received in and removed from the side port. The cannula may also include a cannula liner to prevent the escape of blood from the outlet.
The filter apparatus includes a shaft with an adjustable filter frame disposed about the distal end of the shaft. The frame is adjustable between a contracted condition and an enlarged condition. The filter also includes a frame sizing mechanism and a filter mesh coupled to the frame for capturing embolic material. The filter apparatus may be a stand-alone device or may be removably insertable into the arterial cannula or introducer. Upon insertion through the cannula into the artery, the frame sizing mechanism adjusts the diameter of the filter frame to conform to the inner lumen of the vessel.
Embodiments of the modular filter apparatus include a semi-rigid shaft with some embodiments having a handle on the shaft proximal end. The frame may be metal, plastic, gel or foam or any combination thereof. The filter mesh pore size ideally ranges from 40 to 120 microns, but other sizes may be used depending on the clinical need. The mesh may be plastic, fibrous, or metal, polyester, nylon, Teflon(copyright), or the like, and may be woven, stamped, etched, laser machined, molded, spun or layered. In some embodiments, the mesh is coated with a non-thrombogenic material, for example, heparin, or with a lubricious material. The frame sizing mechanism may be self-adjusting upon deployment, or may be controlled from the proximal end of the shaft. In the former case, for example, the adjustable frame may be formed from a superelastic or shape memory material, such as a Nitinol ring, that opens automatically when deployed. Preferably, the ring includes kinks where the ring is attached to the shaft, biasing the ring against the wall of a vessel, and maximizing the cross-section of the vessel intersected by the filter. Thus, once deployed, the ring automatically expands across the vessel, opening the filter, such as a substantially conical mesh, to capture embolic material in the vessel.
Alternatively, the frame sizing mechanism can be coupled to an external manipulating mechanism associated with the shaft, so that the size of the expansion frame may be externally controlled. For example, the adjustable frame may include an annular inflation seal, such as a silicon balloon, that may be filled with fluid to open the mesh across the vessel into which the device is deployed. In this embodiment, the shaft may include an inflation lumen extending between the proximal and distal ends thereof for injecting and removing fluid.
The frame sizing mechanism may also be mechanically operated, such as by a guide wire or a spring connected to the frame, generally controlled from the proximal end of the shaft. For example, the adjustable frame may include a plurality of struts that may be biased to the contracted condition, possibly using a shape memory material or a spring. A ring attached to the struts may be directed axially to expand and contract the struts respectively between the enlarged and contracted conditions.
Certain embodiments of the modular filter device also include a tubular cartridge into which the expandable filter device may be inserted. Generally, the cartridge is a tubular member providing a hemostatic seal or a one-way valve between the shaft on the filter device and the port on the cannula or the introducer, or the cartridge may include a hemostatic valve to provide a fluid-tight seal between the cartridge and the filter device inserted therein. The cartridge generally has a shape similar to the port, as well as to the shaft on the filter device. Preferably, these components have similar cross-sections, such as a substantially square, rectangular or oval shape, that limit the arterial cannula with modular filter device to a predetermined assembled orientation that ensures that the filter device is deployed across the vessel in the proper orientation. The distal end of the filter is generally inserted into the cartridge, such that the frame and mesh are substantially contained within the cartridge, thereby providing a modular filter cartridge.
The modularity and adjustability of the filter apparatus, combined with its capability of insertion into an introducer or the port of the cannula, are important features in the methods of use that are also described. One method of temporarily filtering embolic material from the blood in a blood vessel includes the steps of first inserting the distal end of the insertion device into a blood vessel, such as the aorta, using conventional procedures. A modular filter apparatus is then inserted into the device and is advanced into the vessel. The frame sizing mechanism is operated to enlarge or contract the adjustable filter frame to conform to the size of the vessel thus opening the filter mesh substantially across the vessel and capturing any embolic material traveling therethrough. At any time, the adjustable frame may be closed to its contracted condition, either automatically by withdrawing the adjustable filter, or by mechanically closing it as described above, entrapping any embolic material captured by the mesh. The adjustable filter may be withdrawn into the insertion device by pulling the shaft proximally, and the filter may then be removed from the device if desired. A new modular filter may be then be inserted into the device, and the new filter introduced into the vessel.
Certain embodiments of the method just described include providing an elongated aspiration tube having a lumen connecting openings in its proximal and distal ends. The proximal end is adapted to connect to an aspiration source and the distal end is slideably insertable into the proximal end of a hollow filter shaft that is also provided. Once the filter is deployed within the vessel, the aspiration tube is slideably inserted through the shaft of the filter until the distal end of the tube lies near the inner surface of the filter mesh. Negative pressure is then applied to the proximal end of the aspiration tube and embolic debris is drawn out of the filter and into the tube. The tube may then be removed from the vessel.
The ability to replace the filter at any time during a procedure is particularly useful in cardiac surgery. For example, a cannula and filter may be deployed as described above within the aorta. The aorta may then be clamped in preparation for a bypass procedure, possibly dislodging embolic material from the wall of the aorta and traveling downstream. With the filter deployed, however, embolic material released during this action may easily be captured by the filter device. Once the aorta is clamped, the risk of embolic material breaking loose is substantially reduced, and so the filter may be removed without substantial concern about embolic material escaping to other areas of the patient.
Later in the surgery, a new filter may be introduced into the aorta when the risk of embolic material becoming dislodged is again increased, as for example when the aorta is unclamped. Because a new filter may be deployed, any embolic material that is dislodged has a much greater likelihood of being captured by the filter without substantially impairing blood flow through the vessel. Thus, a cannula with modular filter apparatus may more effectively capture and remove embolic material released during extended procedures, such as coronary bypass surgery.
Associated devices are also described. For instance, it is often helpful to know in advance the size of the vessel into which a filter is to be deployed. Therefore, a vessel sizing tool is described that includes a vessel sizing shaft that is slideably insertable into a vessel or a hollow vessel insertion device. The shaft has a plurality of visible markings along the shaft indicating units of distance, one of which aligns with an indicator on the insertion device, or with the top of the vessel, when the distal end of the shaft has engaged the wall opposite the insertion point. Other embodiments include a vessel sizing cartridge into which the shaft is inserted.
Methods of using the tool are also described. First, a hollow vessel insertion device adapted to receive a vessel sizing tool and a vessel sizing tool adapted to slideably insert into the insertion device are provided. Next, the distal end of the insertion device is introduced into the vessel. Then the distal end of the vessel sizing tool is slideably inserted into the insertion device, and the tool is advanced through the lumen in the insertion device until the most distal marking on the tool aligns with the indicator on the device, indicating that the distal end of the tool has just entered the vessel. Next, the tool is carefully advanced until the distal end of the tool touches the vessel wall opposite the insertion point, and the visible marking that now aligns with the indicator on the insertion device is noted. This visible marking denotes the depth of the tool in the vessel and thus the vessel diameter.
It is also useful to reduce trauma to the vessel that can be caused by a hollow vessel insertion device and thus an expandable obturator is also described. One embodiment of an obturator includes an obturator shaft that has a tapered distal end, a distal region and an outer surface and a plurality of spaced collet segments arranged coaxially around the distal region of the obturator shaft. Each segment is expandable between a contracted condition and an expanded condition and each segment has an inner surface that conforms to the outer surface of the obturator shaft and a proximal end coupled to the distal region of the shaft. The segment also includes an outwardly flaring elongated member that is expandable away from the outer surface of the obturator shaft. This elongated member forms a collet head at the distal end of the collet segment. The collet head has a proximal end that gradually thickens from the elongated member thereby forming a recess in the region where the elongated member is associated with the collet head. The distal end of the collet head is tapered to a thickness less than the proximal end of the head. This configuration allows the distal end of the insertion device to rest in the recess behind the collet head, and the overall profile of the collet head and distal end of the shaft is smoothly tapered to advance the entering insertion device.
Methods of using the expandable obturator are also described. In one embodiment, the obturator is slideably inserted into the proximal end of the insertion device, causing the collet segments of the obturator to contract about the shaft. The obturator is then advanced through the lumen of the insertion device until the collet heads of the obturator project just beyond the distal end of the insertion device. The collet segments then flare to an expanded condition and the distal end of the insertion device rests in the recesses formed behind the collet heads. The insertion device and associated obturator are then advanced through an incision in the vessel until the distal end of the insertion device enters the vessel. The obturator may then be removed by pulling on the proximal end and causing the proximal portion of the collet heads to slide under the distal end of the insertion device thereby forcing the collet heads to once again assume a contracted condition suitable for removal.
Accordingly, a principal object of the present invention is to provide a modular adjustable blood filter apparatus and delivery system that allows the filter to be decoupled from the delivery system when not needed, and that allows a new filter to be introduced to more effectively capture embolic material within the vessel, such as during an extended surgical procedure.
It is also an object of the present invention to provide an insertion device with modular filter apparatus that substantially minimizes the likelihood of the blood filter becoming clogged and ineffective during use.
Additional objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.